NEW YORK — The operators of the online hangout Facebook wanted to help users save time by highlighting changes their friends make to their personal profile pages. Instead, the new feature has drawn complaints from thousands of its users and even threats of a boycott.

The backlash is over Facebook's decision this week to deliver automated, customized alerts known as News Feeds about a user's closest friends, classmates and colleagues. Users who log on might instantly find out that someone they know has joined a new social group, posted more photos or begun dating their best friend.

"It's making it so much easier for people who want to do stalking to stalk," said Facebook user Igor Hiller, 17, a freshman at University of California, Santa Barbara. "Facebook users really think Facebook is becoming the Big Brother of the Internet, recording every single move."

A protest group created on the site, Students against Facebook News Feeds, had more than 600,000 members by yesterday, and more than 80,000 people had electronically endorsed a petition against the feature. A Web journal has even been set up calling for users to boycott the site on Tuesday, a week after the feature's debut.

"Anytime you're confronted with new information about yourself in a public place, it's surprising," said Andrea Forte, 32, a Facebook user and Georgia Tech doctoral candidate who studies online communities. "My initial reaction was mild dismay."

Facebook has long prided itself on privacy. A user's profile details, including contact information, relationship status and hobbies, are generally hidden from others unless they are already part of that user's network of friends or institution, such as a college.

In addition, users have the option of hiding specific details from certain users, even ones already designated as friends — choosing, for instance, to show photos to college buddies but not to co-workers.

To join, one must prove membership in an existing network using an e-mail address from a college, a high school or selected companies and organizations. As a result, Facebook has fewer than 10 million registered users, compared with some 108 million at News Corp.'s MySpace.

Facebook's chief executive, Mark Zuckerberg, said yesterday that privacy remains central to the site, but he acknowledged the company misstepped and "failed to communicate to our users actively what it actually meant for them."

All of the information presented had been available before, but a person had to visit a friend's profile page and make note of any changes — for example, noticing that the friend now has 103 friends instead of 102, and identifying which one got added.

Zuckerberg said people "can literally spend 10 to 20 minutes going through all the information in individual profiles." The new feature, he said, was meant to "surface the most interesting changes" made by a user's closest friends.

Chris Hughes, co-founder of the two-year-old, privately held company based in Palo Alto, Calif., said Facebook's software analyzes such factors as how often one communicates with a friend or views that friend's profile in determining whom a user deems most important.

He added that anything someone chose to hide to a specific person before would not suddenly appear in that person's feed.

Zuckerberg said Facebook was working on giving users additional privacy options.

The safeguards, expected as early as today, would let users block from feeds entire categories — such as changes to the groups they belong to — while still allowing people to observe such changes by visiting the profile page. Before, a user had to remove items one at a time from their personal feeds.